Nighthawk AX5 RAX30 WAN Port VLAN

Hi

I own a Nighthawk AX5 RAX30 router - currently working fine on Plusnet FTTC utilising PPPoE.

I have ordered FTTP from Connect Fibre recently, due to be installed in a month or so. Whilst getting myself ready for the move, I've seen on their website that if I want to continue to use my own router (which I do) that I need to configure the WAN Port on your third party router to VLAN 101 and DHCP. 

Can anyone offer any guidance as to how I achieve this please? I can't see anywhere in the admin panel how to specifically configure the WAN port.

Thanks